1. Field of the Invention
This invention relates generally institutional dishwashing machines, and more specifically to such machines comprising a circuit for a detergent solution which is highly concentrated in relation to the wash liquor, and which is pump-circulated in a wash zone through the machine load.
2. Discussion of Related Art
In the context of the invention, the expression "machine load" or "dishes" is meant to encompass all the articles to be washed in dishwashing machines, more particularly plates, cups, cutlery and the like. Whereas normal wash liquor typically contains approximately 2 to 6 g detergent per liter of water, a "highly concentrated" detergent solution is one which contains approximately 30 to 80 g detergent per liter water. In institutional dishwashing machines (or IDWMS for short), the machine load is transported, for example on a belt, through various successive zones, more particularly a prerinse zone, a wash zone and a final-rinse zone.
In one known process for washing soiled dishes in a dishwashing machine comprising a wash zone, the prerinsed dishes are treated in the wash zone with a separately circulated, highly concentrated detergent solution. The detergent solution flowing down from the dishes flows into a collecting tank and from there to an external collecting tank or stock liquor container which is followed by a circulating pump supplying the circuit of the detergent solution. In the stock liquor container, the detergent solution is temporarily stored in the circuit. The concentration and amount of detergent solution in the circuit are also restored by controlling the solution in the stock liquor container. This requires sensors and corresponding feed pipes for fresh water and detergent concentrate.
EP-A-0 282 214 describes a process in which highly concentrated detergent solution is sprayed onto the dishes to be washed. This process is carried out in standard dishwashing machines in which a so-called spray arc is installed for spraying the highly concentrated detergent solution. The highly concentrated detergent solution is not collected or circulated separately in a circuit. Accordingly, there is no system separation between the highly concentrated detergent solution and the normally concentrated wash liquor although this would be desirable, for example for further minimizing the consumption of detergent.